Elon Musk should be a happy camper, as it appears that his orbital delivery firm SpaceX has pulled off a successful launch of its third resupply mission to the International Space Station.

SpaceX shoots off the launch pad right on time

The Falcon 9 rocket lifted off from Cape Canaveral on schedule at 12:35pm PDT (8:35pm UTC), carrying 5,000 pounds of supplies for the ISS. The first stage separated cleanly two minutes and fifty one seconds into the flight, 103km above the launch pad, and the Dragon capsule has deployed its solar panels and is now on course to dock with the ISS in two days, once orbital paths have matched up.

It was a very close run thing. The CRS-3 mission was due to take off on Tuesday but was cancelled after a helium leak was detected. Friday's launch was much tighter, and SpaceX said the launch had a one-second window if the rocket was to successfully insert its cargo into the right orbital plane.

Weather was a big worry for the SpaceX team. There was rain and relatively heavy clouds at the launch site, and the team floated multiple weather balloons into the upper atmosphere to make sure that winds weren't too strong at altitude.

Unfortunately, the heavy winds and storm conditions in the Atlantic may hamper the second part of Friday's mission: the remote landing of the first stage of the Falcon 9 rocket. After separating, the booster is planned to fire up again and slow down, falling back towards the Earth.

If all goes well, the rocket will then deploy four legs, which were covered for the initial launch phase, and begin a controlled burn to slowly sink towards the ocean and hover for landing and retrieval. At least, that was the plan.

But the inclement weather means the SpaceX support ship that was due to witness the rocket's return and retrieve the hardware couldn't get into position. SpaceX says it will attempt the soft landing anyway, but there's no word yet on its success or otherwise.

Elon Musk has already said the team isn't expecting to get this tricky landing right the first time, but a successful test flight earlier in the week showed the Falcon 9 was capable of a soft landing. If the technique can be duplicated on an actual launch, it would pave the way for rockets that could be returned to Earth and reused for later flights, slashing the cost of orbital delivery.

It's unpacking time at the ISS

The current CRS-3 mission will now use the Dragon capsule's 18 chemical thrusters to match velocities with the ISS and put itself in position to be grabbed by the space station's Canadian-built robotic arm. This will pull the capsule closer for inspection, before moving it to a docking position with the ISS' Harmony module if everything checks out.

The Dragon capsule separates for its trip to the ISS

The top of the capsule is pressurized and contains perishable supplies, new hardware, and some science experiments, which will be unloaded by the astronauts. A second, unpressurized "trunk" contains two heavier science experiments and these will be unloaded by the robotic arm.

This mission's cargo includes a new spacesuit for the astronauts to use for extra-vehicular activity around the ISS, to replace a malfunctioning suit. Last year European Space Agency astronaut Luca Parmitano nearly drowned during a spacewalk when his cooling system malfunctioned and began to fill his helmet with fluid.

Also on board this Dragon capsule is a pair of legs for the space station's artificial inhabitant Robonaut 2. The NASA-built robot is currently only a torso, but the addition of multi-jointed 4.5ft legs will make it more agile and useful inside and outside the ISS.

If the current resupply mission succeeds, SpaceX will have completed a quarter of its contracted 12 deliveries to the ISS, for which NASA is paying the firm $1.6bn. The space agency is getting some of that money back however, as it has leased the Cape Canaveral Launch Complex 39A, from which Apollo 11 lifted off, back to SpaceX for an unspecified sum.

"SpaceX is the world's fastest growing launch services provider," said Gwynne Shotwell, president of SpaceX. "With nearly 50 missions on manifest, SpaceX will maximize the use of pad 39A to the benefit of both the commercial launch industry as well as the American taxpayer." ®